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Rebuild time... Need help

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So here comes a long explanation just so you guys get the story. I'm sure you can skim and get the main stuff. The bike is a 2013 ktm 250sx

So I bought the bike beginning of season. Rode it. Great compression. Towards mid season I had to mess with the jetting cause it was getting hot and it was set wayyy too rich. So got that figured out. Towards the end of season I started hearing a knocking/tapping/rocks in the pipe noise, something not normal. So at first I thought it was the pipe rattling since it still ran great and had good compression. Changed the o rings, made sure mounts were tight and noise was still there. So skip forward to today after it sitting in the corner. Took the head off no issues. Pull the cylender off and the piston skirts are all scored, one skirt is cracked. And if I line up the rod perfectly dead center there is the slighted bit of up and down play. So I got a couple questions. What Would cause the skirt to crack and score ? And do I need to do a full bottom end rebuild ? Also where the he'll would I find a piston for my size ? Stock bore is 66.4 and stock piston is 66.35 giving a gap of 0.05mm. I measured my cylender quick and got 66.6mm yes ironic haha not funny for me :/ and I can't seem to find any pistons around that size unless I go big bore at 80mm bore.

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Edited by Midnitewarrior4

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So you have a 250 - anyway, piston skirt cracking is generally caused by slap, ie piston is too small for bore. If severe enough parts of the skirt can break off giving you rather serious damage. Do you know how many hours it has done? Unless you have proper equipment you cannot measure the bore yourself, it has a slight taper from bottom to top. There should be no vertical movement in your con rod. Sounds like you need a con rod kit, as well doing the mains and seals at the same time. Depending on the condition of your bore,( ie worn nikasil, can you feel a ridge with your finger nail where the top ring stops at tdc) you may need a replate or a size larger piston. I would suggest a replate needed though. Other may come on with different advice, but that is my diagnosis. Hope this helps, Bob.

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2 hours ago, 7Tktm said:

So you have a 250 - anyway, piston skirt cracking is generally caused by slap, ie piston is too small for bore. If severe enough parts of the skirt can break off giving you rather serious damage. Do you know how many hours it has done? Unless you have proper equipment you cannot measure the bore yourself, it has a slight taper from bottom to top. There should be no vertical movement in your con rod. Sounds like you need a con rod kit, as well doing the mains and seals at the same time. Depending on the condition of your bore,( ie worn nikasil, can you feel a ridge with your finger nail where the top ring stops at tdc) you may need a replate or a size larger piston. I would suggest a replate needed though. Other may come on with different advice, but that is my diagnosis. Hope this helps, Bob.

Yeah somehow missed putting in what my bike was... Its a 2013 250sx. No clue on hours. I'm on a really tight budget. Honeslty just want to fix this bike so I can get it out of my shed. Things been a nightmare. Do you know if I would just be able to buy bearings or would I have to buy a whole kit with the crank. If so I'm kinda screwed. Can't afford to be putting a 1000$ rebuild in this bike. Also what would a replays consist of ?. As for measurement of the cylender I'll be borrowing some measurement tools this week to get a better measurement 

8 hours ago, GlennRay said:

Can you give us a clue as to what kind of bike this is?

Sorry.it's a 2013 250 sx 

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Shouldn't be a nightmare unless it has had a tough life through lack of maintenance. They are real good bikes, but need some attention now and again. Re the wear in your rod bearing - you just can't have any up and down. If (when) the bearing lets go it can cause a lot of damage.  You have to renew the bearing together with a new rod. Oem KTM is 300$ and fitting to loose crank around 50$. I just suggested your mains as well but they may well be fine. Def worth renewing the seals though which are real cheap when the crank is out. You've not said what condition your cylinder is - have you checked for a detectable ridge near the top, is it scored and does it look a different colour of grey above the exhaust port. It may be that you can get a good after marked rod kit - perhaps a 250 owner will come on and say what is good/bad. We only run 125s and always use oem. Surely a 13 250 sx is worth looking after and spending some money on.  Bob.

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Unless you ride it like a pro I would consider giving Cooksey a call, unfortunaly it seem he doesnt do cranks until 15th oct. Do some research on him youself, https://www.cookseycrank.com/crank-rebuild . He got some top end kits too from Vertex. Never heard anything bad about him/his work.

If you split the cases I would change the main bearings anyway, cheapest part to rebuild on bottom end anyway.

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Good input from Wessmen. Andrew Cooksey has a great reputation - I tried to get a team together to kidnap him and Grant Langston and bring them to the UK lol. You might also look inside your piston skirt. OEM KTM has the words 'KTM' and 'Vertex' cast inside. Aftermarket Vertex only has 'Vertex'. While it isn't definitive (obviously) most people (us included) just fit the aftermarket Vertex (but same great quality) as it is much cheaper than the oem. Might be a clue if the piston has ever been changed from new but to be fair you can normally get real high hours out of a 250 piston. Bob.

Edited by 7Tktm

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9 hours ago, 7Tktm said:

Good input from Wessmen. Andrew Cooksey has a great reputation - I tried to get a team together to kidnap him and Grant Langston and bring them to the UK lol. You might also look inside your piston skirt. OEM KTM has the words 'KTM' and 'Vertex' cast inside. Aftermarket Vertex only has 'Vertex'. While it isn't definitive (obviously) most people (us included) just fit the aftermarket Vertex (but same great quality) as it is much cheaper than the oem. Might be a clue if the piston has ever been changed from new but to be fair you can normally get real high hours out of a 250 piston. Bob.

It's a cheapo namura piston. The only thing is I can't find a dam piston the size I need.... Obviously this bike has seen some big abuse. From my rought measurement. Still have to get some tools From a. Friend at work to get a good measurement my cylinder is 0.2mm larger then stock which is just way to much clearance from piston to cylender which is probably what cause the piston to crack in the first place. I've tried looking everywhere I could think of. Tried every search combination all I could come up with was stock size or the big bore 270sx kit.... I'm just a trail rider/ pit banger. Not a racer so honestly I don't have a budget for anyone else to work on my bike but me. Really unfortunate but way she goes for me. Can't really find any places that sell just the bearing And or bearing and just the rod. Everywhere I see it's a complete crank kit. And again Definetly not in the budget. First time owning a two stroke and it's Definetly not going well to far

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13 hours ago, 7Tktm said:

Shouldn't be a nightmare unless it has had a tough life through lack of maintenance. They are real good bikes, but need some attention now and again. Re the wear in your rod bearing - you just can't have any up and down. If (when) the bearing lets go it can cause a lot of damage.  You have to renew the bearing together with a new rod. Oem KTM is 300$ and fitting to loose crank around 50$. I just suggested your mains as well but they may well be fine. Def worth renewing the seals though which are real cheap when the crank is out. You've not said what condition your cylinder is - have you checked for a detectable ridge near the top, is it scored and does it look a different colour of grey above the exhaust port. It may be that you can get a good after marked rod kit - perhaps a 250 owner will come on and say what is good/bad. We only run 125s and always use oem. Surely a 13 250 sx is worth looking after and spending some money on.  Bob.

Cylender isn't scored but it's pretty worn at this point. The forum will probably link my two replies together or maybe not so I'll just sumarize again. Cylinder is at 66.6mm vs 66.4mm. Stock says max 0.1mm piston to cylender clearance and the largest piston I can find so far is a 66.35 which in a good cylender would be perfect... But if I could find a piston in the 66.55 or Even a 66.6 and I could bore out a touch and be good that would be sweet.doesn't seem to be a big ridge at the top. But I'll have to see when I'm able to measure different points in the cylinder. I'm new to 2 stroke bikes but not to 2 strokes in general.

Oh and for reference on lack of proper maintenance. The guy was too lazy to even buy car motor oil for the tranny that he used the left over of his dominator mixing oil in the trans.... 

Edited by Midnitewarrior4
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15 minutes ago, Midnitewarrior4 said:

Cylender isn't scored but it's pretty worn at this point. The forum will probably link my two replies together or maybe not so I'll just sumarize again. Cylinder is at 66.6mm vs 66.4mm. Stock says max 0.1mm piston to cylender clearance and the largest piston I can find so far is a 66.35 which in a good cylender would be perfect... But if I could find a piston in the 66.55 or Even a 66.6 and I could bore out a touch and be good that would be sweet.doesn't seem to be a big ridge at the top. But I'll have to see when I'm able to measure different points in the cylinder. I'm new to 2 stroke bikes but not to 2 strokes in general.

Oh and for reference on lack of proper maintenance. The guy was too lazy to even buy car motor oil for the tranny that he used the left over of his dominator mixing oil in the trans.... 

LOL, this just made my day. I feel for you though bro. I prob have 1500$+ into my Yz250 after last owner neglected the bike bad. I don't mind though since it will be better than new when I am done with it. Also it's fun to wrench ;)

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Hmm. I still think you are inaccurate with your measurements of the cylinder.  The simple solution is to get it replated - we use Langcourt in the UK - they are subsidiary of the parent company in the USA. There will be similar companies as well . They will  replate your cylinder to stock size and it will be as good as new - they take a little extra for welding any deep gouges etc. The cylinder then comes back to you as good as new - they even sand blast the outside. Some customers include the new piston they wish to use (usually size 1 or A) so it is matched to it. We don't bother with this as their work is so accurate. Cost wise we pay around 270 of your dollars including delivery for what is in effect a brand new cylinder. Don't even consider a rebore - it cannot be done. Bob.

Edited by 7Tktm
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9 hours ago, Christoffer Brandel said:

LOL, this just made my day. I feel for you though bro. I prob have 1500$+ into my Yz250 after last owner neglected the bike bad. I don't mind though since it will be better than new when I am done with it. Also it's fun to wrench ;)

Yeah. I go to change the oil. Comes out thick and red..... Look over and see the gas in the race can he have me red.... No way.... Get a water bottle and ful it with the oil..... Yup he did that.IMG_20170417_182808.thumb.jpg.cf1979c3579c26944466f90af7bf77ea.jpg

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4 hours ago, 7Tktm said:

Hmm. I still think you are inaccurate with your measurements of the cylinder.  The simple solution is to get it replated - we use Langcourt in the UK - they are subsidiary of the parent company in the USA. There will be similar companies as well . They will  replate your cylinder to stock size and it will be as good as new - they take a little extra for welding any deep gouges etc. The cylinder then comes back to you as good as new - they even sand blast the outside. Some customers include the new piston they wish to use (usually size 1 or A) so it is matched to it. We don't bother with this as their work is so accurate. Cost wise we pay around 270 of your dollars including delivery for what is in effect a brand new cylinder. Don't even consider a rebore - it cannot be done. Bob.

I'll have to look into it. I'm in Canada so not sure what companies are around but I think I might know a place. They redo nikisil coatings and deal with snowmachine motors but I'm sure they do bike motors too

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3 hours ago, Scoutin Wyo said:

That might be ATF in the transmission. That's my optimistic side talking...emoji15.png

Yeah... Unfortunately no.... Took quite a few oil changes to flush that Crap out. 

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Mongoose in Vancouver does replating. Just had my 300 jug done a couple months ago.
As for the nightmare abused ktms can be, I'm right there with you. Bought my 09 300xc last October and have been on it 8 times, every time it came home needing something fixed. Just did a replate and wiseco piston and next ride out the clutch slave blows. It's been non stop repairs to this thing and it's still needs a bunch of work to get it 100%.
Anyways I'm betting yours needs a replate, I think I paid somewhere around $600 for the plating and piston/rings/gaskets and did the work myself

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St-Pierre Moteur in Quebec does replating, likely closer for the OP located in Ontario.

Link: https://www.stpierremoteur.com/home

 

OP, you might be on a tight budget but cutting corners will end up costing a lot more in the end.

Failing to properly refurb the bottom end will likely end up destroying your newly rebuilt top end.  

 

Owning an MX race bike on a tight budget most often does not end well.

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38 minutes ago, mlatour said:

St-Pierre Moteur in Quebec does replating, likely closer for the OP located in Ontario.

Link: https://www.stpierremoteur.com/home

 

OP, you might be on a tight budget but cutting corners will end up costing a lot more in the end.

Failing to properly refurb the bottom end will likely end up destroying your newly rebuilt top end.  

 

Owning an MX race bike on a tight budget most often does not end well.

I found a place called cv tech. Going to measure my cylinder and get it sent out for a replate. The only reason I'm really on a budget for tge is my plan is pretty much fix it and get rid of it as fast as possible and I just don't want to be dumping money into it for nothing. And really to have to do a rebuild every year possibly and have to pay to get it replated every couple rebuilds just seems like a major waste of money... I love the bike but I Definetly can't afford to keep doing rebuilds like this every year

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53 minutes ago, dittohead said:

Mongoose in Vancouver does replating. Just had my 300 jug done a couple months ago.
As for the nightmare abused ktms can be, I'm right there with you. Bought my 09 300xc last October and have been on it 8 times, every time it came home needing something fixed. Just did a replate and wiseco piston and next ride out the clutch slave blows. It's been non stop repairs to this thing and it's still needs a bunch of work to get it 100%.
Anyways I'm betting yours needs a replate, I think I paid somewhere around $600 for the plating and piston/rings/gaskets and did the work myself

Ya so far I've had to do a tire, I rebuilt the clutch slave and master because they were starting to go, rejet it and mess with the carb for days, it needs brake rotors, sprockets, chain, rear suspension bearings/bushings... I've had to weld new brackets for the exhaust cause the guy dropped it and snapped them... Great bike when it's running.... Only got 16 hours on it all season. Maybe got out 6 times.... Was planning on putting at least 50 hours on. 

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